Indoor pollutants are generally classified into two categories based on their physical size and properties: gas phase pollutants and particle phase pollutants. Gas phase pollutants are chemical molecules or vapors which are in molecular size. Particle phase pollutants are particulate matter or bacteria which are in a few to hundred micron size.
Traditionally, air purification involves the use of a HEPA, an ionizer, and/or an electrostatic precipitator for the removal of particulate matter and airborne bacteria.
To further reduce the gas phase pollutants, adsorbent materials such as activated carbons and molecular sieves can be employed. These gas removal filters can be collectively grouped as adsorption filters. Adsorption filters are usually characteristic with high filter air flow resistance when closely packed. In some cases, a photocatalyst filter together with a UV source for volatile organic compounds decomposition are employed. Gas removal filters utilizing a method involving a decomposition reaction that occurs on the catalyst surfaces can be collectively grouped as catalyst filter. A characteristic of some catalyst filters is low filter air flow resistance.
In a conventional air purification system, a blower is used to draw or blow the air from the upstream to the downstream. Generally, the air is brought to pass through the first few layers for particulate matter and airborne bacteria removal and subsequently the layers in the downstream position for gas phase pollutants removal.
This layer by layer design enables the gas phase pollutants to be removed effectively only at the early stage. As no particle filter would be able to remove the particulate matter completely; the un-removed particulate matter would fall into the second, third, fourth layers and so on. Over time, the gas removal adsorption filters become ineffective in the later stages because they become saturated and due to clogging on the adsorption surface by the buildup of particulate matter. If a catalyst filter is used, it can fail to properly function and is unable to decompose the gas phase pollutant molecules. This is because the buildup of particulate matter from upstream layers contaminates the surface of the catalyst and prevents it from adsorbing reactant for reaction. Therefore, the catalytic surface becomes poisonous and ineffective.
The traditional design of removing particulate matter and gas phase pollutants by a single blower also creates a fundamental problem. The high air flow rate is beneficial only for the particulate matter removal. A high airflow rate increases the number of times for particulates to pass through the particle filter and hence the number of particulates being caught is increased. Nevertheless, the high air flow rate is unfavorable for gas phase removal. This is because the adsorption and absorption of gas phase pollutants in adsorption filter or adhesion of pollutants on surface of catalyst filter for chemical decomposition requires time. They work best only in slow air flow rate, which would lengthen the residence time. In other words, there exists a contradiction on the “optimum need of airflow rate” for particulate matter removal and gas phase pollutants removal.
As a result, traditional air purification techniques which target particulate matter and gas phase pollutant removal, requires the use of layers by layers and including a single blower. This leads to problems that: shorten the lifetime of the gas removal filters and the effectiveness of the particle removal filter and also the gas removal filter is difficult to optimize at the same time.
To address the above problem, Japanese patent application 2004-74859 has a special design using a damper for switching the air flow path and branches the downstream into either an ion generation electrode path or into a filter based on the concentration of dust in the environment. If a catalytic filter is used in place of the downstream opening 9b, the design preserves the life catalytic filter. This is because the damper closes the catalyst filter and allows only dust removal. When the dust level concentration is low, the damper closes the dust removal filter and opens the catalyst filter. However, the design is inflexible and unable to treat air properly if the environment is polluted with both high concentrations of gas phase and particle phase pollutants. Moreover, in the design, a blower is installed at the upstream position. The air is blown onto a filter instead of drawn into a filter. The filter with high filter air flow resistance is undesirable because air would return back instead of passing through the filter smoothly when the air is blown onto it.
Referring to FIG. 1, a prior art air purification system is shown. In the prior art air purification system, a blower 1 is used to draw or blow air 6 from an upstream position to a downstream position. Generally, air passes through the first few layers 2-3 for particulate matter and airborne bacteria removal and subsequently the layers 4-5 in the downstream position for gas phase pollutant removal.
Referring to FIG. 2, a modified prior art air purification system is shown according to the principle disclosed in Japanese patent application 2004-74859. Japanese patent application 2004-74859 has a special design which includes a damper 7 for switching air flow path and branches the downstream path into either an ion generation electrode path or into a filter path based on the concentration of dust in the environment. A catalytic filter 8 is used in place of the one down stream opening and a dust removal filter is used in place of the “filter”